A balanced diet for triathletes looks a little different from that of the general population. The discrepancy is partly in amounts, which we've already talked about. Triathletes need to eat more -- more carbohydrates, more protein and more good fats (not saturated or trans) in order to balance a greater energy output.

But it also may differ in the proportional balance of nutrients, and that can vary by the day. A longer training session means increased energy requirements, and that means increased intake of carbohydrates, the body's quickest source of energy. This is where "carb loading" comes in. It starts several days before the race and involves a major shift in calorie sources.

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The purpose of carb loading is to load up the muscles with glycogen, energy derived from carbohydrates, so they're overstuffed when race day arrives. Normally, muscles have enough stored glycogen to maintain about 90 minutes of intense exercise; successful carb loading will increase that by 200 percent to 300 percent [source: MTP]. The added energy helps sustain the more intense and much longer energy output of the triathlon, helping to delay the inevitable muscle fatigue that comes with that kind of expenditure.

At the same time, training activities decrease in the days leading up to event. As the muscles are resting and putting out less energy, nutritional energy inputs are increasing. The result is a highly energized body on race day.

Still, no matter how much energy is waiting, it won't be enough for the entire triathlon. Triathletes have to eat (and drink) during the race. Nutritional timing during the race, as well as in training and recovery, is critical.